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Buellia stellulata
Buellia stellulata, commonly known as the disc lichen[1]) is a species of crustose lichen that is widely distributed throughout the Northern Hemisphere.[2] MorphologyThallusThe thallus is crustose, areolate, and thin to moderately thickened, often forming a continuous layer. The prothallus is conspicuous and black, strongly developed in most specimens, growing between the areoles to form a hypothallus. The thallus surface is usually white to whitish gray, rarely dark gray, and can be dull or slightly shiny. The thallus is epruinose and phenocorticate, and lacks soredia.[3][4] MedullaThe medulla is white and lacks calcium oxalate.[3] ApotheciaThe apothecia exhibit a lecideine structure, with a diameter ranging from (0.2-)0.3-0.4(-0.5) mm. They are typically immersed to adnate, occasionally found in a sessile form. The margin may appear black or masked by grayish remnants of necrotic thalline material, forming a thin and usually persistent boundary, occasionally excluded as they mature. The disc is characterized by a black, epruinose surface, typically flat but occasionally developing a slight convexity over time. Within the apothecia, the proper exciple appears narrow and lacks differentiation, resembling the aethalea-type. The inner excipular hyphae are narrow, hyaline, and often prosoplectenchymatous, exhibiting structural and orientational similarities to the paraphyses. The hypothecium is characterized by a deep reddish-brown color, described as leptoclinos-brown with a textura intricata. Outer excipular hyphae are arranged parallelly, moderately swollen (textura oblita), and heavily carbonized, displaying a range of brown shades and aeruginose pigments.[4][3] EpihymeniumThe epihymenium is brown, with pigmentation continuous with the outer exciple.[3] HymeniumThe hymenium is hyaline and not inspersed with oil droplets. The paraphyses are simple to moderately branched, with apically swollen tips containing a brown pigment cap.[3] Asci and ascosporesThe asci are clavate, Bacidia-type, and 8-spored. The ascospores soon become brown, 1-septate, oblong to ellipsoid, usually not constricted, with obtuse ends, and not curved, measuring (8-)8.7-[9.9]-11.1(-13) x (4.5-)4.8-[5.5]-6.1(-7) μm. The proper septum is narrow and does not thicken during spore ontogeny (Buellia-type). The spore ornamentation is microrugulate.[3] ChemistryThe lichen contains the secondary metabolites atranorin, 2'-O-methylperlatolic acid,[a] and confluentic acid. Spot tests are K+ yellow (sometimes weak), P- or + faintly yellow, C-, KC-, and CK-. UV fluorescence is -(dark).[3] Substrate and ecologyBuellia stellulata, an epilithic lichen, thrives on siliceous rock surfaces (typically HCl-) and is commonly found in coastal regions. However, its habitat is not restricted solely to seashore environments.[3] DistributionBuellia stellulata exhibits a broad distribution across the Northern Hemisphere. Within the Sonoran region, this species is notably present in coastal areas spanning from southern California to Baja California and Baja California Sur.[3][2] See alsoNotes and referencesNote
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